The preparation of a composition based on thermoplastic polymers and vulcanized rubbers, according to the method of dynamic vulcanization, is known in the prior art and is described in particular in U.S. Pat. Nos. 3,758,643; 3,862,106; 3,037,954 and 3,806,558.
According to the above mentioned method, the vulcanization of the elastomeric component is made to occur during the mixing or mastication with a molten plastomeric polymer, by the aid of cross-linking agents which in general are of conventional type, such as for instance peroxides, azidic compounds, mixtures of sulfur with zinc oxide, substituted ureas, thiocarbamates, etc. If in the mix which is thus treated there is present a sufficient quantity of plastomeric polymer, the composition, at the end of the vulcanization of the elastomeric component, will maintain good processability properties under heat even at high percentages of vulcanized elastomer.
According to French Patent No. 2,408,632, plastic-elastomeric compositions may be obtained by dynamical vulcanization methods, using as a cross-linking agent a halogenated phenolic resin, or a non-halogenated resin, however associated to halogen-donors in combination with a metal oxide (activator).
According to said French Patent, the mix of EPDM rubber and olefinic polymer with the phenolic resin in a proportion of from 5% to 20%, with respect to the rubber, is, subjected to a temperature sufficient for melting the olefinic polymer, thereafter the activator is added in a quantity generally not higher than 0.6% by weight of the total, and thereupon carrying on the mastication at a temperature at which the cross-linking of the elastomeric component occurs.
However, the compositions obtained by the dynamical vulcanization method show, as a feature common to all the compositions based on mixes of plastomeric polymers with cross-linked elastomers, the drawback of being so much more difficult to be processed or heat-moulded, the higher the percentage of cross-linked elastomeric component present in these compositions.